1. Field of the Invention
The present invention relates to a coordinate measuring instrument which is composed of a main part and a controller, wherein the main part in which a work to be measured and a probe sensor are three-dimensionally movable relative to each other, while the controller is capable of driving the main part in accordance with a predetermined procedure so as to measure the shape and size of the work by making use of the amount of relative movement between the work and the probe sensor. The invention also is concerned with a method of generating pattern data concerning the shape of the work to be measured.
2. Description of the Related Art
FIG. 10 shows a typical known coordinate measuring instrument. The measuring instrument is composed mainly of a main part 31 and a controller 51. The main part 31 includes various parts such as a base 32, supporting posts 34, 34 on both sides of the base 32, a beam 35 extending between both supporting posts 34, 34, an X-slider 36 capable of sliding in X-direction along the beam 35, a Z-guide box 37 integrally attached to the X-slider 36, a spindle 38 guided by the Z-guide box for sliding motion in Z-direction, a work table 42 reciprocally movable on the base 1 in Y-direction, Y-direction driving means and Y-direction displacement detector placed under the work table 42, side plates 33, 33 and bellows 46 for shielding the Y-direction driving means and the Y-direction displacement detector from dusts and other contaminants, and a touch signal probe 44 attached to the lower end of a spindle 38 and provided with a sensor 45. A reference numeral 43 designate a probe holder frame capable of holding a plurality of types of touch signal probes 44, 44, 44. Although not shown, an automatic probe changer is provided to automatically change the touch signal probe 44 on the spindle 38.
The controller 51 is constituted mainly by a control unit 52, a console 53 for allowing various setting and instructing operations, and an output system 54 which is provided with a typewriter and/or a CRT for outputting the result of the measurement. The control unit 52 stores predetermined measuring programs which provide procedures for determining shape and size of a work 1 on the work table 42, by making use of relationships existing between the probe sensor 45 and the work 1, e.g., positions or points where they are mutually engaged, number of the points where they are engaged, and the amount of relative movement between the work 1 and the probe sensor 45.
In operation, the work 1 to be measured is mounted on the work table 42 and a predetermined measuring program corresponding to the type of the work 1 to be measured is set in the control unit 52 of the controller 51, whereby the apparatus gets ready for the automatic measuring operation. As the automatic measuring operation is commenced, the work table 42, X-slider 36 and the spindle 38 are driven in a predetermined procedure, so that the probe sensor 45 and the work 1 to be measured are three-dimensionally moved relative to each other. During this relative movement, the probe sensor 45 and the work 1 to be measured are made to be engaged with each other. In this case, since the probe 44 is of the touch signal type, the term "engaged with" should be interpreted as indicating "directly contacted by" each other. When the probe sensor 45 and the work 1 are brought into contact with each other, the probe 44 produces a touch signal. By using such touch signals obtained at numerous points of contact between the probe sensor 45 and the work 1, it is possible to determine the amount of relative movement between the probe sensor 45 and the work 1 and, hence, to precisely determine the shape, size and other factors of the work 1 by the measuring program.
The basic construction and the operation principle are the same also in the cases where the main part 31 is modified such that the work table 42 is fixed rather than being moved and where the probe sensor 45 is of an optical sensor capable of recognizing the work without making direct contact therewith.
The described coordinate measuring instrument, however, suffers from the following problems.
For attaining a prompt and accurate automatic measuring operation by this coordinate measuring instrument, it is essential that the measuring procedure corresponding to the type of the work 1 is programmed and stored. The programming of the measuring procedure has been conducted typically by teaching method or playback method. For instance, such a known programming method comprises the steps of preparing a reference work which is a precisely finished model of the work 1 to be measured, setting the reference work on the work table, operating the main part 31 manually or semi-automatically so as to relatively move the reference work and the probe sensor 45 to enable them to be engaged with each other thus executing the measuring procedure, and reading and storing data such as amount of the relative movement, positions and number of the points where they are engaged, and so forth, whereby the program is formed by using such numerical data. Thus, the programming of the measuring procedure essentially requires preparation of the reference work, with the result much time and money are spent uneconomically particularly when a multiplicity of reference works have to be prepared to comply with demand for measurement of a multiplicity of types works. Obviously, the necessity for the preparation of such reference works seriously impairs the efficiency of the measurement.
In recent years, systems such as CAD (computer-aided design) and CAM (computer-aided manufacture) are becoming popular for automation of designing and manufacturing processes with the aid of computers. Such computer-aided systems, however, have been excluded from the process for measurement and inspection of the products, due to various restrictions from the user's point of view. Thus, numerical data available for the design and manufacture could not be utilized in the measurement and inspection of products. This undesirably limits the efficiency of production including design, manufacture and inspection. In addition, the coordinate measuring instrument may fail to effectively function depending on the type of the work to be measured.
As explained above, the programming of the measuring procedure has to be done for each type of the work to be measured by employing a reference work. The process for building up the numerical data, however, tends to vary according to the individual who manipulates the measuring instrument, with the result that the precision and the efficiency are impaired. In addition, the programming is necessary for each type of the work to be measured, even if the difference in the shape and size between different types of work are slight.